Glass substrate for magnetic disk and method for producing the same

Abstract

The present invention relates to a method for producing a glass substrate for a magnetic disk, the method including a step of polishing a main surface of a circular glass plate while supplying a polishing slurry containing a polishing material, in which polishing is performed, after a polishing surface is subjected to dressing treatment, by using a polishing pad having: a first resin foam layer which forms the polishing surface, includes a resin foam having pores with a pore diameter of more than 20 μm and has a thickness of 400 μm or less; and a second resin foam layer which is provided between a platen for fixing the polishing pad and the first resin foam layer, includes a resin foam having pores with a pore diameter of 20 μm or less and has a thickness of 50 to 250 μm, and in which a total thickness of the first resin foam layer and the second resin foam layer is 550 μm or less, and a international rubber hardness degree of the polishing pad measured by the M method according to JIS K6253 is 40 IRHD or more.

1. A method for producing a glass substrate for a magnetic disk, said method comprising a step of polishing a main surface of a circular glass plate while supplying a polishing slurry containing a polishing material,
 wherein polishing is performed, after a polishing surface is subjected to dressing treatment, by using a polishing pad having: a first resin foam layer which forms the polishing surface, comprises a resin foam having pores with a pore diameter of more than 20 μm and up to 40 μm has a thickness of 300 to 350 μm; and a second resin foam layer which is provided between a platen for fixing the polishing pad and the first resin foam layer, comprises a resin foam having pores with a pore diameter of 10 to 20 μm and has a thickness of 75 to 200 μm, 
 and wherein a total thickness of the first resin foam layer and the second resin foam layer is 375 to 550 μm, and a international rubber hardness degree of the polishing pad measured by the M method according to JIS K6253 is 42 to 50 IRHD. 
 
     
     
       2. The method for producing a glass substrate for a magnetic disk according to  claim 1 , wherein the second resin foam layer has a compressibility at 200 μm of 3% or less. 
     
     
       3. The method for producing a glass substrate for a magnetic disk according to  claim 1 , wherein an open pore area ratio of the polishing surface is adjusted to 8% or more, and an average circle equivalent diameter of open pores of the polishing surface is adjusted to 10 μm or more, by the dressing treatment. 
     
     
       4. The method for producing a glass substrate for a magnetic disk according to  claim 1 , wherein after a surface layer of the polishing pad is cut off by the dressing treatment, brush cleaning is performed while supplying pure water. 
     
     
       5. The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the first resin foam layer and the second resin foam layer are joined through a joining solution. 
     
     
       6. The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the polishing material is a colloidal silica or a fumed silica. 
     
     
       7. The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the first resin foam layer comprises polyurethane. 
     
     
       8. The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the second resin foam layer comprises polyethylene terephthalate. 
     
     
       9. The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the total thickness of the first resin foam layer and the second resin foam layer is 375 to 500 μm. 
     
     
       10. The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the second resin foam layer has a thickness of 100 to 200 μm. 
     
     
       11. The method for producing a glass substrate for magnetic disk according to  claim 1 , wherein the international rubber hardness degree of the polishing pad measured by the M method according to JIS K6253 is 46-49 IRHD.